Slip rings have long been employed in applications where electrical power must be provided to an electrically powered device which is in intermittent or constant rotation relative to the power source. Normally the slip rings are mounted on the rotating element with a brush module fixedly mounted in conjunction with the power source and in proximity to the slip rings and having an individual brush element in engagement with each of the rings of the slip ring assembly. There are, of course, numerous different applications where slip rings have been commonly used, with the slip rings being designed to take into account particular facets of the environment or the operating conditions under which the apparatus operates. In most applications there is considerable latitude in terms of the design of a slip ring assembly in that size, weight, cost and related considerations are not subject to stringent limitations.
In a general sense, slip rings have characteristically been manufactured by methods requiring a substantial number of machining operations, many of these operations requiring precise equipment and/or workmanship. In some instances the respective slip rings have been initially machined to the appropriate dimensions. Thereafter, a metallic disk or base is machined to accurate tolerances for the mounting of the assembly and a portion of the disk or base is then cut away in precise areas to receive the slip rings. The cut-away areas characteristically are filled with an electrically nonconductive molding material such as a plastic which forms a holding element for the rings and simultaneously forms insulating elements around the slip rings in the form of an insulating backing and concentric insulating elements disposed between the spaced rings. It is reportedly difficult to arrange rings accurately concentrically of the base and maintain nearly perfect alignment during the molding operations. Subsequent significant machining is needed to remove molded nonconductive plastic material from the rings and to produce the necessary true concentric position and close tolerance flat face. In addition, certain plastics employed as slip ring insulating materials have highly different coefficients of expansion than the slip rings and the metallic base such that the finished ring assembly may be subject to warping with temperature variations during processing or thereafter.
Another approach to the manufacture of slip rings involves the use of a molded plastic disk or plate which is machined to contain concentric grooves. Individual slip rings are fabricated and inserted in the concentric grooves to be secured as by cementing. It is reportedly difficult to obtain a sufficiently precise match between the size of rings and the grooves and to maintain the rings sufficiently accurately concentric. A modification of this method contemplates an electro deposit of metal to fill the machined grooves of the plastic base. The machining of the plastic is still required and the plastic base is likely to become contaminated with the plating solution and degrade the electrical insulating properties of the plastic in electro depositing or comparable complex processes.
In order to overcome the quality control problems associated with processes of the type discussed above the art has resorted to even more complex and extensive machining operations to achieve the extent of accuracy and quality control required of slip ring assemblies. An example of such a process is the formulation of deep grooves in a disk of material where the intermittent ribs are to constitute the slip rings, the deep grooves forming intermittent ribs projecting from a retained base. The grooves are subsequently filled with an insulating material and a backing member or plate is attached covering the grooves and the ribs. Thereafter the original base which maintained the ribs in true spaced concentricity is entirely machined away to leave the ribs projecting from the later attached backing member or plate. This process has the obvious disadvantage of wasting great quantities of material and requiring extensive machining steps.
It is thus believed that prior art processes have not achieved the potential for construction of highly accurate slip ring assemblies which can be manufactured without numerous and normally extensive machining steps requiring highly skilled craftsmanship. This has apparently remained the situation despite numerous efforts toward the development of more accurate and sophisticated slip ring assemblies.
A further problem attendant the manufacture of slip ring assemblies is the attachment of studs normally at spaced intervals around a slip ring to which electrical connections from the power supply are subsequently attached. In some instances studs are attached by welding or soldering operations which with or without associated protective structure may become damaged or separated from the slip ring during shipping, installation or in the operational environment for the slip ring assembly. In other instances, slip rings may be made removable by securing them to a base with screws or by effecting a crimping of a projecting post. Since ring elements thus mounted are subject to accidental loosening or removal, temporary fastening elements of this nature are not normally considered to be appropriate for high performance, close tolerance applications.